The last thing Bishan Rajapakse remembered before everything went black was paddling towards a 40-foot whale off Bondi Beach and inquiring of the giant mammal: "Hey, how's it going?"

Mr Rajapakse, a New Zealand doctor, was among a dozen or so surfers transfixed by the whale - said to be "the size of a bus" - which surfaced close to the beach this morning and frolicked among them, before giving a flick of its gigantic tail.

The flick "just sent the surfers flying like skittles", said one witness, Lachlan Harris, who was watching from a nearby clifftop. Mr Rajapakse, 38, came off worst of those tossed into the air, losing consciousness for about 15 seconds and coming to only after being transported to dry land by other surfers.

Paramedics strapped him into a neck brace in case of spinal injuries, and rushed him to hospital. By afternoon, he was sitting up in bed, with no injuries apart from "a slight headache".

The whale - reported variously to be a humpback or southern right whale - cruised within 75 yards of the rocks at the southern end of Bondi Beach, according to lifeguards. As surfers surrounded it, "the whale was frolicking with them, and having a lot of fun, and sort of popping its head out", Mr Harris told the ABC.

One surfer, Jeremy Piggin, said: "He just kept swimming around and looking at us … It was as if he wanted to play with us." A friend dived down to get a closer look, "and saw the whale's flippers nearly dragging along the sand … It was that shallow."

Sri Lankan-born Mr Rajapakse paddled over. "When I got to him, I saw there was this dark, black shadow, and it was just massive," he told the Sydney Morning Herald. "The whale was moving in like slow motion. It was beautiful, and it breached, and … it was slowly going up and down, and turning, and it actually made a noise."

The tail flick tossed him about ten feet in the air, and smashed his surfboard. Another lifeguard, Anthony Carroll, commented: "The tail of a whale is the strongest muscle on any animal in the world … It's an extreme no-no to go in the vicinity of a whale."

The whale remained off Bondi for about two hours, and was last seen heading north, under the escort of a police boat and three jet skis.